1. Field of the Invention
The present invention relates to a method of manufacturing a line of autohesion thread in which adjacent filaments are substantially fused together.
2. Background of the Invention
Fishing lines for leisure and fishery, materials for fisheries such as a longline of tuna fishery, and threads to be employed for rope, gut or kite string are roughly divided mainly into monofilament yarn and braided yarn such that plural monofilaments are braided.
Monofilament yarn has low frictional resistance in rubbing against other matters because it has a smoother surface than braided yarn. For example, when using monofilament yarn as a fishing line, the frictional resistance caused by the rubbing of the fishing line and the guide in throwing in the fishing line is so low that bait can be thrown exactly to a long distance. Monofilament yarn is also superior in drainability because it holds no water inside. In addition, braided yarn is cut with difficulty, and when the yarn is cut, the yarn in the cut portion is split and the cut portion becomes feathery, so that the handling is difficult. Monofilament yarn also has an advantage in that it has no such problem. However, for example, in the case where resin composing the yarn is ultra high molecular weight polyethylene or fully aromatic polyamide, it is necessary to use a solvent in spinning, and to remove the solvent after spinning. This is a problem that it is difficult to manufacture a monofilament having a certain thickness or more, which is appropriate for uses such as a fishing line, rope or gut as described above.
On the other hand, braided yarn can be made into a line of thread having a thickness appropriate for uses as described above, irrespective of the kind of resin as a raw material, by reason of employing plural monofilaments or a multifilament. In addition, braided yarn has such an advantage that it is possible to combine plural kinds of filaments. As a result, an effect such as adjustment of desired specific gravity, which is not obtained in a single filament, can be attained. In monofilament yarn, it is naturally impossible to combine plural kinds of filaments.
JP-A-9-98698 reports a method of manufacturing a fishing line in such a manner that plural filaments of polyolefin are braided or twisted, and thereafter exposed to a temperature in the melting range of polyolefin while drawn at a draw ratio of 1.0 or more to thereby fuse adjacent filaments. The inventors of the present invention, however, have found out that it is practically difficult to substantially fuse adjacent filaments in the above-mentioned fishing line by such a method. Accordingly, the application of physical force by use to the fishing line thus manufactured disjoints the bond of fiber by reason of not being actually substantially fused, so that it is incapable of achieving the original object of making a pseudo monofilament by fusing. The problem is that the application of physical force by use causes the fishing line to have no differences with ordinary braided yarn. Further, the inventors of the present invention have found a defect such that heat treatment in such a method decreases the strength of the fishing line, which thus cannot but be drawn in order to compensate for the decreased strength. Consequently, the drawing compensates for the strength, while the fishing line becomes greatly thinner to the extent of the thickness of approximately 60% or less compared to the thickness of the fishing line before the treatment, thereby deteriorating wear resistance.
The inventors of the present invention have earnestly studied a yarn having the above-mentioned advantages of both monofilament yarn and braided yarn to develop a line of thread in which plural filament yarn of high strength fiber are integrated by using low-temperature thermal adhesion resin having a lower melting point than the melting point of the above-mentioned filament yarn (JP-A-2002-54041). As a result of extensive studies, they have also developed a line of thread in which low-temperature thermal adhesion resin is replaced with a hot melt adhesive (JP-A-2003-116431).